The invention relates to a polymeric multilayer film having a high percentage of pigments, or other fillers. Pigments are often added to a thin polymeric film to increase opacity, whiten the film or otherwise modify the optical properties of the film. Other fillers are added to polymeric films to provide bulk, or otherwise decrease the cost of the film. One problem associated with adding high levels of fillers to a polymeric matrix is the resulting adverse effect on material properties such as tear strength, tensile strength and softness which often occurs. The adverse effect on material properties often constrains the percentage, or concentration, of fillers, such as opacifying and whitening pigments, added to a polymeric film.
For example, U.S. Pat. No. 4,521,437 issued to Storms June 4, 1985, teaches that pigment loadings limited to 15 weight percent can be obtained without adversely affecting the material properties of the film. U.S. Pat. No. 3,154,461 issued to Johnson Oct. 27, 1964 teaches a polymeric film having up to 25 weight percent particulate material. However, this teaching further requires biaxial stretching of the film at a temperature above the polymer second order transition temperature to produce opacity. U.S. Pat. No. 3,900,670, issued to Ikeda et al. Aug. 19, 1975 discloses a multilayer film having 26 to 50 weight percent fillers. However, this reference also requires biaxial stretching to produce opacity as a result of voiding within the film.
The opacity and whiteness of a thin film are, therefore, limited by the concentrations of opacifying and whitening pigments added to the film. Stretching of the film, to cause opacity, adds a step to the manufacturing process which is reflected in increased cost.